This invention relates generally to electronically controlled fuel injection systems and, more particularly, to thermal damage protection of the electronic circuitry associated with the control and operation of an engine.
Electronically controlled fuel injectors for engines are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from associated electronic circuitry. These signals include waveforms that are indicative of a desired injection rate as well as the desired timing and quantity of fuel to be injected into the cylinders of the engine. Historically many fuel injection systems include a single main fuel injection, or shot, to the cylinder for each fuel injection event. More recently, split injections, post injections, and other multiple injection events are contemplated for use in an engine. In such configurations, each waveform may consist of one, two, three, or perhaps more, distinct and/or rate-shaped fuel shots to a cylinder during a particular fuel injection event.
Signals corresponding to the fuel injection waveforms, or fuel shots, are typically generated by electronic circuitry associated with a controller or other processing means commonly used to control the operation of the engine. Such circuitry typically controls the quantity of fuel delivered to each fuel shot associated with a particular injection waveform as well as the timing between the number of fuel shots and other parameters. The engine thereafter performs in accordance with the injector waveform signals thus received. Those skilled in the art will appreciate that the electrical load on the circuitry generating such signals will directly correspond to the frequency of the injection waveforms and the number of fuel shots in the waveforms. As the speed on the engine increases, the frequency of the waveforms will also increase, and therefore the frequency and number of fuel shots generated by the circuitry in a given time interval will likewise increase. Such increase in the firing frequency of fuel injection signals typically corresponds directly to an increase in the temperature of the circuitry due to the increase in performance thereof. If the temperature of the control circuitry increases and rises above a threshold level, various components of the electronic circuitry may be irreparably damaged.
As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
Aside from engine speed or the firing frequency of the fuel injection shots, the temperature of the circuitry may rise above a threshold level due to other reasons as well. For example, when the voltage level of the power source providing electrical power to the circuitry drops below normal, or below a threshold level, the current delivered to the respective electronic components must be increased to compensate for the lower voltage in order to continue providing the same amount of electrical power to the injectors or other engine components. Higher current through the circuitry typically results in a higher circuit board temperature. Even a small drop in the voltage level of the power source from normal may result in an increase in the current sufficient to raise the temperature of the circuitry to a level at which the circuitry may be susceptible to thermal damage. Although it is possible to redesign and reengineer the circuitry to perform at higher current or higher power levels, such redesign and reengineering would be expensive and would add to the overall manufacturing costs of the engine.
It is therefore desirable to determine engine conditions or other criteria indicative of when the temperature of the electronic control circuitry associated with the engine control system increases, or has the propensity to increase, above a threshold level, and it is desirable to provide protection means to such circuitry to prevent damage thereto.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method and apparatus is disclosed for the protection of the electronic circuitry associated with the operation of an engine, including the electrical and electronic components thereof, against thermal damage during certain engine operating conditions. An increase in the fuel injection frequency or engine control circuitry temperature above a threshold level for a certain period of time may cause thermal damage to the circuitry. This elevated temperature may be determined in any one of a variety of ways. For example, in a multi-shot fuel strategy, the frequency of the fuel shots delivered to the engine in a specific period of time will increase due to engine speed or engine load. Accordingly, as the engine speed increases for example, the frequency and number of current pulses generated and delivered to the fuel injection system by the fuel injector control circuitry within a specific period of time also increases. Generating a greater number of electrical current pulses may result in an increase in the overall temperature of the circuitry, including an increase in the temperature of the electrical or electronic components forming the overall control module. Accordingly, an electronic control module (ECM) is operable to monitor engine speed and/or other engine performance parameters and, based thereupon, can determine, correlate, or otherwise establish if the corresponding temperature of the electronic circuitry is approaching or has reached a predetermined threshold level.
Alternately, the ECM may also monitor the voltage level of the power source providing electrical power to the electronic circuitry associated with the engine. A drop in the voltage level of the power source below a normal or threshold voltage level will typically correspond to an increase in the amount of heat generated in the electronic circuitry because, if the voltage decreases, the amount of current provided by the power source must be increased in order to maintain the required amount of electrical power necessary to meet engine requirements. Accordingly, the ECM can determine or otherwise establish whether the temperature of the circuitry has exceeded a predetermined threshold level based upon a predetermined decrease in the voltage level of the power source.
Still further, a temperature sensor may be provided in proximity to the electronic circuitry associated with the engine control system, which temperature sensor is operable to sense the present or actual temperature of the circuitry and to output a signal indicative thereof. The temperature sensor is coupled to the ECM whereby the ECM will receive the signal emitted by such sensor and, based upon such temperature signal, will determine whether the temperature of the circuitry has exceeded a predetermined threshold level.
The ECM may be programmed to perform any one or more of a number of different actions to protect the electronic circuitry from thermal damage resulting from an undesirably high temperature. Under one such action, the ECM may restrict the number of fuel shots delivered by the circuitry to the fuel injectors of the engine during a fuel injection event. If the firing frequency of the multiple fuel shots are too high for a specific period of time, the electronics will get too hot. In this situation, in a three shot fuel injection system, for example, the ECM may limit the number of fuel shots in a particular fuel injection event to just one shot, or perhaps two shots. A reduction in the number of fuel shots will decrease the number of electrical pulses generated by the electronic circuitry thereby reducing the amount of thermal energy and heat generated by the circuitry which in turn reduces the overall temperature of the circuitry.
In another embodiment, the ECM may restrict the performance or operation of the engine in order to protect the electronic circuitry from thermal damage. In this case, the engine will not perform as requested by the operator, but will only perform at a reduced capacity, such as at a reduced speed, irrespective of the performance commanded by the operator. Reduced performance of the engine will translate into a reduced amount of electrical signals generated by the electronic circuitry, and therefore a decrease in the temperature associated therewith.
Depending upon what triggered the potential circuitry overheat situation, the restrictions imposed upon the engine""s performance in an effort to help protect the circuitry associated therewith from thermal damage may be removed once the temperature of the circuitry returns to within predetermined threshold limits. On the other hand, depending upon the triggering event, the imposed restrictions may not be removed and it may be mandatory for an operator to have the engine or work machine serviced in order to correct the underlying problem. This may be true in the case of a low battery voltage condition where the battery, or alternator, or charging system must be replaced before any restriction on the engine""s performance is removed.
In yet another embodiment, the event which triggered the present protection control system may be recorded in an appropriate memory or data recordation means associated with the ECM whereby a service technician may retrieve such information and data when the engine is serviced at a later time. Based upon such information, the service technician may properly investigate and repair the underlying cause which triggered the rise in the circuitry""s temperature.